1. Field of the Invention
This invention relates to a suspension for a steerable driving wheel in a vehicle and, more particularly, to a suspension in a vehicle provided with a wheel carrier rotatable around a steering axis, a hub for transmitting a driving force from a drive shaft to a wheel, and a brake disk for transmitting a brake force generated in cooperation with a brake caliper to the hub.
2. Description of the Prior Art
As one of suspensions for a steerable driving wheel, there is a strut type suspension as shown in FIG. 9 (for instance, as described in "Repairs for Vista" issued Mar. 24, 1982 by Toyota Jidosha Kabushiki Kaisha, on Page 3-33).
In the suspension, a wheel carrier 10 has an upper portion firmly fixed to a strut 11, and the strut 11 is swingably supported to a vehicle body 13 through a support 12. The wheel carrier 10 has a lower portion swingably connected to a suspension arm 15 through a ball joint 14. Thereby, the wheel carrier 10 is permitted to rotate around a steering axis L (king pin axis) interconnecting the center O.sub.1 of the support 12 and the center O.sub.2 of the ball joint 14.
On the other hand, a drive shaft 16 is unrotatably connected to a hub 17 rotatably supported by the wheel carrier 10 through a bearing (not shown), and a disk wheel 18 of a wheel and a brake disk 19 are attached to the hub 17. The brake disk 19 generates a braking force in cooperation with a brake caliper (not shown).
The point where a rotary axis of a tire 20 and a vertical plane passing through the center of the grounding contact surface of the tire 20 intersect each other is defined as I point where, and a point the rotary axis of the tire 20 and the steering axis L intersect each other in a condition to be projected on a surface parallel to the surface of FIG. 9 is defined as K point the driving force from the drive shaft 16 acts on the rotary axis of the tire at the time of driving of the vehicle, and a moment proportional to the I-K distance is generated by the driving force to make the tire tend to rotate around the steering axis L. Accordingly, since a steering wheel or handle is forced to be moved, a so-called steering effort is necessary to resist it.
The I-K distance has to be made small in order to lessen the steering effort. For that end, the center O.sub.1 of the support 12 or the center O.sub.2 of the ball joint 14 may be located laterally as outward as possible of the vehicle. However, it is difficult to change the position of the center O.sub.1 of the support 12 by reason of the spacial restriction in a car room or an engine room, or the prevention of interference of the strut 11 with the tire 20. Also, the center O.sub.2 of the ball joint 14 is naturally limited in bringing its position outward in consideration that the brake disk 19 is located laterally outward of the ball joint 14 and the disk wheel 18 is incapable of varying its shape since the disk wheel 18 requires interchangeability.
There is a double wishbone type suspension (Japanese Patent Publication No. 52-9889), in which a wheel carrier is supported by two upper links swingably connected to two portions of the wheel carrier located longitudinally at an interval above a rotary axis of a wheel, and two lower links swingably connected to two portions of the wheel carrier located longitudinally at an interval below the rotary axis of the wheel. According to the double wishbone type suspension, the line interconnecting respective imaginary intersections of two upper links and two lower links functions as an imaginary steering axis.
The above-mentioned strut type suspension has the extremely small degree of freedom in design of the steering axis for making the I-K distance small. The conventional double wishbone type suspension involves the similar problem to that of the strut type suspension.
In case of the double wishbone type suspension as described in the above publication, in which the wheel carrier rotates around the imaginary steering axis, the I-K distance can be made small. On the other hand, rotation of the wheel carrier around the imaginary steering axis means that the connection points of the wheel carrier and the links are displaced to make the wheel carrier rotate around the imaginary steering axis seemingly. Thus, the alignment of the wheel is varied with the steering operation.